Japanese Patent Publication No. 2921654 discloses a coupling device used for the above application. Such a coupling device includes a socket (immovable female coupler) and a plug (movable male coupler). Conduits are connected to the socket and the plug, respectively.
The socket is equipped with a circumferential side flange. By attaching the side flange to a mount panel, the socket is secured while being connected to the conduit. When the plug connected to the other conduit is inserted into the socket, the plug and the socket are arranged in a line. With an operation of an inner mechanism built in the socket previously, the respective conduits of the socket and the plug are communicated with each other, so that fluid is transferred.
However, when the conduit is connected to the plug, and fluid is transferred for a relatively long period of time while the plug is inserted into the socket, the plug is subjected to a moment of force due to the weight of a flange or the like attached to the rear end of the plug. As a result, there is a possibility that not only the valve sealing characteristics of the plug, but also the sealing characteristics of the socket deteriorate.
Additionally, the plug is required to be inserted into the socket every time fluid is transferred, a portion of the plug engaging the socket is easily worn.
This invention has been achieved in view of the above situation, and an object thereof is to provide a plug for a fluid-transfer coupling device, which can be firmly supported in the socket, especially, even when the flow rate of fluid is relatively large.